Axial fan apparatus, housing, and electronic apparatus

ABSTRACT

An axial fan apparatus including an axial-flow impeller, a drive unit, and a housing. The axial-flow impeller is capable of rotating and includes a plurality of blades inclined with respect to a rotational axis direction. The drive unit rotates the axial-flow impeller. The housing is mounted with the drive unit, and includes a sidewall, and a plurality of slits that circulate gas. The sidewall is provided around the axial-flow impeller. The plurality of slits are provided to the sidewall and inclined with respect to the rotational axis direction in a direction opposed to a direction in which the plurality of blades incline.

RELATED APPLICATION DATA

This application is a continuation of U.S. patent application Ser. No.12/101,558, filed Apr. 11, 2008, the entirety of which is incorporatedherein by reference to the extent permitted by law. The presentapplication claims priority to Japanese Patent Application No. 07-107749filed in the Japanese Patent Office on Apr. 17, 2007, the entirety ofwhich also is incorporated by reference herein to the extent permittedby law.

BACKGROUND OF THE INVENTION

The present invention relates to an axial fan apparatus that blows airin an axial-flow direction, a housing that is used for the axial fanapparatus, and an electronic apparatus that is mounted with the axialfan apparatus.

Recently, fans are used to cool down heat generators in most electronicapparatuses such as PCs. Herein, it is necessary to increase flow rateof the fans and to reduce noise generated by the operating fans.

Japanese Patent Application Laid-open No. 2001-003900 (paragraphs 0016and 0017, FIG. 1; hereinafter referred to as Patent Document 1)discloses an axial-flow fan including a housing (5) surrounding a fanrotor (1). Lateral slits (14) are formed to the housing (5). A width ofthe slits (14) is set such that laminar flows of air are generated.Patent Document 1 describes that, with this structure, generation ofturbulent flows and noise are suppressed.

SUMMARY OF THE INVENTION

In order to suppress the noise, the fans should preferably be furtherimproved. In addition, decreased noise level is strongly requested byusers.

In view of the above circumstances, there is a need for an axial fanapparatus and a housing capable of suppressing noise, and an electronicapparatus mounted with the axial fan apparatus.

According to an embodiment of the present invention, there is providedan axial fan apparatus including an axial-flow impeller, a drive unit,and a housing. The axial-flow impeller is capable of rotating andincludes a plurality of blades inclined with respect to a rotationalaxis direction. The drive unit rotates the axial-flow impeller. Thehousing is mounted with the drive unit, and includes a sidewall, and aplurality of slits that circulate gas. The sidewall is provided aroundthe axial-flow impeller. The plurality of slits are provided to thesidewall and inclined with respect to the rotational axis direction in adirection opposed to a direction in which the plurality of bladesincline.

In general, when an axial-flow impeller rotates, there generate airflows(hereinafter referred to as swirling flows) in the vicinity of an endportion of a blade from a surface (air discharge side) opposed to anegative pressure generation surface side (air suction side) of theblade to the negative pressure generation surface side. The swirlingflows generate noise. According to this embodiment, when the axial-flowimpeller rotates, air flows from the outside of the housing to theinside via the plurality of slits. Since the plurality of slits areinclined in the direction opposed to the direction in which the bladesare inclined, the swirling flows are straightened. The noise can thus besuppressed.

In this embodiment, each of the plurality of blades includes an endportion at an outer circumferential side of rotation, a negativepressure generation surface that generates a negative pressure, and anauxiliary vane standing on the negative pressure generation surface atthe end portion. Accordingly, the generation of the swirling flows inthe vicinity of the end portions of the blades as described above can besuppressed. With the result, the noise can further be suppressed.

In this embodiment, the auxiliary vane has a height from the negativepressure generation surface smaller than twice a thickness of each ofthe plurality of blades. In the case that the height of the auxiliaryvane is too large, when the axial-flow impeller rotates, air sucked viathe slits into the housing tends to flow toward the negative pressuregeneration surface of the blade but is shielded by the auxiliary vanes.In this case, the function for straightening the swirling flows by theslits is deteriorated. However, since the height of the auxiliary vanesfrom the negative pressure generation surface is smaller than twice thethickness of the blades as described above, the swirling flows arestraightened owing to the slits and suppressed owing to the auxiliaryvanes in a balanced manner, and the noise level is decreased.

In this embodiment, the sidewall includes an annular innercircumferential surface and an annular outer circumferential surface.That is, the sidewall has substantially the constant thickness. Thus,compared to a sidewall including an annular inner circumferentialsurface and a plane outer surface, i.e., a sidewall having excessivethickness, the sidewall of this embodiment can have the slits having alarger entire opening area. The housing including the sidewall havingthe excessive thickness is generally a rectangular parallelepiped inmost cases. Compared to the case that the slits, for example, are formedto the plane outer surface, the annular sidewall of this embodiment canhave the slits larger in number. The suction amount and flow rate of thegas can thus be increased.

According to another embodiment of the present invention, there isprovided a housing provided to an axial fan apparatus including anaxial-flow impeller including a plurality of blades inclined withrespect to a rotational axis direction, and a drive unit that rotatesthe axial-flow impeller. The housing includes a mount portion and asidewall. To the mount portion, the drive unit is mounted. The sidewallis provided around the axial-flow impeller, and has a plurality of slitsthat circulate gas. The plurality of slits are inclined with respect tothe rotational axis direction in a direction opposed to a direction inwhich the plurality of blades incline.

According to another embodiment of the present invention, there isprovided an electronic apparatus including a casing and an axial fanapparatus. The axial fan apparatus includes an axial-flow impeller, adrive unit, and a housing. The axial-flow impeller is capable ofrotating and includes a plurality of blades inclined with respect to arotational axis direction. The drive unit rotates the axial-flowimpeller. The housing is mounted with the drive unit and disposed in thecasing, and includes a sidewall, and a plurality of slits that circulategas. The sidewall is provided around the axial-flow impeller. Theplurality of slits are provided to the sidewall and inclined withrespect to the rotational axis direction in a direction opposed to adirection in which the plurality of blades incline.

As described above, according to the embodiments of the presentinvention, noise can be suppressed and flow rate can be increased.

These and other objects, features and advantages of the presentinvention will become more apparent in light of the following detaileddescription of best mode embodiments thereof, as illustrated in theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view showing an axial fan apparatus according toan embodiment of the present invention;

FIG. 2 is a plan view showing the axial fan apparatus of FIG. 1 seenfrom a back surface side thereof;

FIG. 3 is a side view of the axial fan apparatus of FIG. 1;

FIG. 4 is a diagram illustrating functions of a blade and swirlingflows;

FIG. 5 is a diagram for comparing an inclination of a slit and that ofthe blade;

FIG. 6 is a perspective view showing a general axial fan apparatus inthe past;

FIG. 7 is a perspective view showing an axial fan apparatus in which anannular sidewall of a housing is provided with a plurality of circularvent holes;

FIG. 8 is a graph showing measurement results of a P-Q characteristic(and a noise level characteristic) regarding the axial fan apparatus ofFIG. 1, the axial fan apparatus of FIG. 6, and the axial fan apparatusof FIG. 7;

FIGS. 9A, 9B, and 9C show data of the graph of FIG. 8;

FIG. 10 is a perspective view showing an axial fan apparatus accordingto another embodiment of the present invention;

FIG. 11 is a diagram illustrating functions and effects of an auxiliaryvane;

FIG. 12 is a graph showing measurement results of a P-Q characteristic(and a noise level characteristic) regarding an axial fan apparatusincluding an axial-flow impeller without auxiliary vanes, and axial fanapparatuses respectively including three kinds of axial-flow impellershaving auxiliary vanes different in height;

FIG. 13 is a diagram illustrating respective heights of the auxiliaryvanes of the three axial fan apparatuses;

FIGS. 14A and 14B show simulation for determining positions of noisesources when the blades including the auxiliary vanes rotate;

FIGS. 15A and 15B show simulation illustrating pressure distribution ofair when the blades including the auxiliary vanes rotate; and

FIG. 16 is a schematic perspective view showing an electronic apparatusaccording to another embodiment of the present invention, specifically,a desktop PC.

DESCRIPTION OF PREFERRED EMBODIMENTS

In the following, embodiments of the present invention will be describedwith reference to the accompanying drawings.

FIG. 1 is a perspective view showing an axial fan apparatus according toan embodiment of the present invention. FIG. 2 is a plan view showingthe axial fan apparatus of FIG. 1, denoted by reference numeral 10, seenfrom a back surface side thereof. FIG. 3 is a side view of the axial fanapparatus 10.

The axial fan apparatus 10 includes a housing 3 and an axial-flowimpeller 5. The axial-flow impeller 5 is capable of rotating inside thehousing 3. The axial-flow impeller 5 includes a boss unit 6 and aplurality of blades 7. A motor (drive unit; not shown) is built in theboss unit 6. The plurality of blades 7 are provided around the boss unit6.

The housing 3 includes an annular sidewall 35. An opening at an upperportion of the sidewall 35 serves as a suction port 3 a. Airflows in anaxial direction (Z direction) generated by the blades 7 rotating in a θdirection are sucked into the housing 3 via the suction port 3 a. Asshown in FIG. 2, a discharge port 3 b is provided to a lower portion ofthe sidewall 35. The discharge port 3 b discharges the gas sucked viathe suction port 3 a. The gas is typically air, but may be of anotherkind. Hereinafter, the gas is assumed to be air. It should be noted thata mount plate 2 is provided to the lower portion of the sidewall 35. Themount plate 2 is used in the case of mounting the axial fan apparatus 10to a given position in an electronic apparatus. The mount plate 2 isprovided with screw holes 2 a. The axial fan apparatus 10 is mountedthereto with screws.

As shown in FIG. 2, a hold plate 4 is disposed to the discharge port 3b. The hold plate 4 is coupled to ribs 9 and serves as a mount portionto which the motor is mounted. The mount portion may have any shapeinstead of a plate shape as in the case of the hold plate 4. A circuitboard (not shown) that drives the motor is provided onto the hold plate4. The motor is arranged onto the circuit board and inside the boss unit6.

The sidewall 35 of the housing 3 is provided with a plurality of slits35 a via which the gas is circulated. As shown in FIG. 3, the pluralityof slits 35 a incline with respect to a rotational axis direction (Zdirection) of the axial-flow impeller 5 in a direction opposed to adirection in which the blades 7 incline. As shown in FIG. 3, the blades7 incline from bottom left to top right with respect to the rotationalaxis direction.

The slits 35 a are provided by predetermined pitches in a rotationalcircumferential direction (θ direction) of the axial-flow impeller 5.The pitch can arbitrarily be set. The pitch may be set depending on awidth u of the slit 35 a and a diameter R (refer to FIG. 2) of thesidewall 35 of the housing 3. All the slits 35 a have substantially thesame widths u. In the case that, for example, the diameter R of thesidewall 35 is 40 to 60 mm, the width u of the slit 35 a is 1 to 2 mm.However, they are not limited to the above. Alternatively, the slits 35a may have different widths u depending on positions.

The blade 7 includes a negative pressure generation surface 7 a at thesuction port 3 a side, and a back surface 7 b opposed to the negativepressure generation surface 7 a. The negative pressure generationsurface 7 a generates laminar flows of the gas, to thereby generate anegative pressure, and is curved. So, in a precise sense, theinclination of the blade 7 refers to an inclination of a tangent line ata given point on the curved negative pressure generation surface 7 a,specifically, an inclination of the tangent line in the rotationalcircumferential direction of the axial-flow impeller 5 with respect tothe rotational axis direction. Alternatively, the inclination of theblade 7 may be an average inclination of a plurality of tangent lines.

Meanwhile, the inclination of the slit 35 a with respect to therotational axis direction refers to an inclination α of the slit 35 a ina longitudinal direction with respect to the rotational axis direction.The inclination α of the slit 35 a is an inclination from bottom rightto top left. The inclination α of the slit 35 a is opposed to theinclination of the blade 7 closest to the slit 35 a with respect to therotational axis direction. The inclination α of the slit 35 a withrespect to the rotational axis direction is larger than 0° and smallerthan 90°. The inclination α is typically 30° to 60°, specifically, 45°.

The axial-flow impeller 5 is typically made of a resin, but may be madeof metal, rubber, or the like. The housing 3 is also typically made of aresin, but may be made of other materials.

Functions of the axial fan apparatus 10 structured as described abovewill be described.

The driving of the motor causes the axial-flow impeller 5 to rotate. Therotational direction of the blades 7 is counterclockwise seen from thetop surface side of FIG. 1. As shown in FIG. 4, the rotation of theaxial-flow impeller 5 generates airflows A on the negative pressuregeneration surface 7 a of the blade 7, to thereby generate a negativepressure in the vicinity of the negative pressure generation surface 7a. Thus, airflows are generated from the suction port 3 a of the housing3 in the axial-flow direction, and the air is discharged from thedischarge port 3 b.

As shown in FIG. 4, since a negative pressure is generated in thevicinity of the negative pressure generation surface 7 a, the airflowsgenerally tend to flow into the negative pressure generation surface 7 aside from the back surface 7 b side of the blade 7 via an end portion 7c on an outer circumferential side of the blade 7. That is, eddy flowsare generated. Hereinafter, the eddy flows are referred to as swirlingflows C. The swirling flows C generate noise. In this case, since thenegative pressure is generated in the vicinity of the negative pressuregeneration surface 7 a, air is flown from the outside of the housing 3into the inside of the housing 3 via the slits 35 a of the housing 3.Since the slits 35 a incline in the direction opposed to the inclinationdirection of the blades 7, the air took in the housing 3 via the slits35 a straighten the swirling flows C and the straighten airflows B aregenerated as shown in FIG. 5. That is, the generation of eddy flows issuppressed, and thus the noise is suppressed.

In addition, according to this embodiment, as shown in FIG. 1, thesidewall 35 has an annular shape, that is, includes an annular innercircumferential surface 35 b and an annular outer circumferentialsurface 35 c. The sidewall 35 thus has a substantially constantthickness d1. Owing to this structure, compared to a sidewall 135including an annular inner circumferential surface 135 b and a planeouter surface 135 c as shown in FIG. 6, i.e., the sidewall 135 havingexcessive thickness, the sidewall 35 can have the slits 35 a having alarger entire opening area. Note that FIG. 6 is a perspective viewshowing a general axial fan apparatus in the past. A housing 103including the sidewall 135 having the excessive thickness is generally arectangular parallelepiped in most cases. Compared to the case that theslits 35 a, for example, are formed to the plane outer surface 135 c,the annular sidewall 35 of this embodiment can have the slits 35 alarger in number. The suction amount and flow rate of the gas can thusbe increased.

FIG. 7 is a perspective view showing an axial fan apparatus in which anannular sidewall 85 of a housing 53 is provided with a plurality ofcircular vent holes 85 a. FIG. 8 is a graph showing measurement resultsof a P-Q characteristic (flow rate-static pressure characteristic) and anoise level characteristic regarding the axial fan apparatus 10 of thisembodiment shown in FIG. 1 (axial fan apparatus A), the axial fanapparatus shown in FIG. 6 (axial fan apparatus C), and the axial fanapparatus shown in FIG. 7 (axial fan apparatus B). In this experiment,design values of the axial fan apparatuses A, B, and C are as follows.

(1) Axial fan apparatus A

-   -   Diameter of sidewall: 40 mm    -   Entire opening area of slits 35 a: 476 mm²    -   Inclination θ of slits 35 a: 45°

(2) Axial fan apparatus B

-   -   Diameter of sidewall: 40 mm    -   Entire opening area of vent holes: 414.5 mm²

(3) Axial fan apparatus C

-   -   Length of one side of sidewall of housing 3: 40 mm

It should be noted that, in each of the axial fan apparatus A, B, and C,the diameter of the axial-flow impeller is smaller by 0.5 to 2 mm thanthe diameter of the sidewall, or, in the item (3), than the length ofone side of the sidewall 135 of the housing 103.

Generally, the axial fan apparatuses operate with flow rate of ±(10 to20)% with half the maximum flow rate as a standard (hereinafter referredto as “operating point range”). To be specific, an intersection point ofthe P-Q curve and a system impedance curve (not shown) may, in mostcases, be an operating point (e.g., 0.95). In the graph, the flow rateof the three axial fan apparatuses A, B, and C is, for example, 0.06 to0.10 m³/min in the operating point range.

In the operating point range, the axial fan apparatus A of thisembodiment represents the highest static pressure. That is, in theoperating point range, the flow rate of the axial fan apparatus A (10)is larger than those of the axial fan apparatuses B and C when it isassumed that those axial fan apparatuses represent the same staticpressure. In addition, in the operating point range, the noise level ofthe axial fan apparatus A is the lowest, and that of the general axialfan apparatus C in the past is the highest of the three. The noise levelof the axial fan apparatus A is lower by 9 to 10 dB than that of theaxial fan apparatus C.

It should be noted that FIGS. 9A, 9B, and 9C show data of the graph ofFIG. 8.

FIG. 10 is a perspective view showing an axial fan apparatus accordingto another embodiment of the present invention. In the following,description of members, functions, and the like similar to those of theaxial fan apparatus 10 of the above embodiment shown in FIG. 1 and otherfigures will be simplified or omitted. Members, functions, and the likedifferent from those of the axial fan apparatus 10 will mainly bedescribed.

In the axial fan apparatus of this embodiment, denoted by referencenumeral 20, each blade 17 of an axial-flow impeller 15 is provided withan auxiliary vane 18. The auxiliary vane 18 stands on a negativepressure generation surface 17 a at an end portion 17 c (refer to FIG.11) at an outer circumferential side of rotation of the blade 17.Typically, the auxiliary vane 18 stands from a horizontal plane (X-Yplane) by substantially 90 degrees. However, the angle may be set to 70to 110 degrees, or may be set to an angle outside that range.

Further, the housing 3 has the same structure as that of the housing 3of the above embodiment. The sidewall 35 includes the slits 35 a. Theinclination of the slits 35 a is opposed to an inclination of the blades17.

Since each blade 17 includes the auxiliary vane 18 as described above,the swirling flows C are straightened. For example, as shown in FIG. 11,the swirling flows C are suppressed and laminar flows D are generatedalong the auxiliary vane 18. Noise is thus suppressed.

The height of the auxiliary vane 18 from the negative pressuregeneration surface 17 a (height of a portion of the auxiliary vane 18from the negative pressure generation surface 17 a, the portion beingmost distant from the negative pressure generation surface 17 a) is notlimited as long as the auxiliary vane 18 does not contact the othermembers. Specifically, in the case that the height of the auxiliary vane18 is smaller than twice the thickness of the blade 17 from the negativepressure generation surface 17 a, the noise level can further bedecreased, which will be described below.

FIG. 12 is a graph showing measurement results of a P-Q characteristic(and a noise level characteristic) regarding an axial fan apparatusincluding an axial-flow impeller without the auxiliary vanes 18, andaxial fan apparatuses respectively including three kinds of axial-flowimpellers having the auxiliary vanes 18 different in height. In theexperiment described referring to FIG. 12, the axial fan apparatusincluding the axial-flow impeller without the auxiliary vanes 18 isdenoted by D. In addition, the three axial fan apparatuses are denotedby E, F, and G in the descending order of the height of the auxiliaryvanes 18. The axial fan apparatus D used in the experiment describedreferring to FIG. 12 is designed substantially similar to the axial fanapparatus A used in the experiment described referring to FIG. 8. Theaxial fan apparatuses E, F, and G are obtained by employing theauxiliary vanes 18 having different height in the axial fan apparatus A.

FIG. 13 is a diagram illustrating an auxiliary vane 18E of the axial fanapparatus E, an auxiliary vane 18F of the axial fan apparatus F, and anauxiliary vane 18G of the axial fan apparatus G. A blade of anaxial-flow impeller of the axial fan apparatus E is denoted by referencesymbol 17E, a blade of an axial-flow impeller of the axial fan apparatusF is denoted by reference symbol 17F, and a blade of an axial-flowimpeller of the axial fan apparatus G is denoted by reference symbol17G. A height t1 of the auxiliary vane 18E of the axial fan apparatus Eis the largest of the three, and is larger than three times a thicknesst0 of the blade 17E. A height t2 of the auxiliary vane 18F of the axialfan apparatus F is larger than the thickness t0 of the blade 17F, butsmaller than twice the thickness t0 (2×t0). A height t3 of the auxiliaryvane 18G of the axial fan apparatus G is smaller than the thickness t0of the blade 17G.

The graph of FIG. 12 teaches as follows. In the operating point range,the static pressure of the axial fan apparatus E including the auxiliaryvane 18E largest in height is lower than that of the axial fan apparatusD without auxiliary vanes, specifically, is the lowest of the four.However, the noise level of the axial fan apparatus E is the lowest ofthe four. When the axial fan apparatuses F and G are employed, thestatic pressure can be increased while the noise level can be decreased.In other words, the auxiliary vane 18F having the height t2 and theauxiliary vane 18G having the height smaller than the height t2 arepreferable. Specifically, the auxiliary vane 18G having the height t3 ismost preferable.

FIGS. 14A, 14B, 15A, and 15B are diagrams each showing simulation of astate of fluid in the vicinity of the auxiliary vane 18G having theheight t3 or the auxiliary vane 18F having the height t2 and the slit 35a of the housing 3. FIGS. 14A and 14B show simulation for determiningpositions of noise sources. FIGS. 15A and 15B show simulationillustrating pressure distribution of air. FIG. 14A shows the auxiliaryvane 18G, FIG. 14B, the auxiliary vane 18F, FIG. 15A, the auxiliary vane18G, and FIG. 15B, the auxiliary vane 18F.

As shown in FIGS. 14A and 14B, a noise source is generated in thevicinity of a side surface of an outer circumferential surface of eachof the auxiliary vanes 18G and 18F. The noise source area in the case ofthe auxiliary vane 18G is smaller than that in the case of the auxiliaryvane 18F. However, in the case of the auxiliary vane 18G, a noise sourceis generated inside the slit 35 a.

As shown in FIGS. 15A and 15B, the auxiliary vane 18F having the heightt2 suppresses the swirling flows C more effectively than the auxiliaryvane 18G. Meanwhile, since the auxiliary vane 18G has the height t3smaller than the height t2, low pressure area generated in the vicinityof the negative pressure generation surface 17 a of the blade 17Gexpands to the vicinity of the slit 35 a as shown in the dotted circle Hof FIG. 15A. That is, the pressure difference is large in the vicinityof the slit 35 a. Accordingly, in the case of the auxiliary vane 18Ghaving the height t3, the swirling flows C are suppressed owing to theslit 35 a.

In view of the above, the height of the auxiliary vane 18 from thenegative pressure generation surface 17 a is preferably smaller thantwice the thickness of the blade 17. With this structure, the swirlingflows C are straightened owing to the slit 35 a and suppressed owing tothe auxiliary vane 18 in a balanced manner, the flow rate is increased,and the noise level is decreased.

FIG. 16 is a schematic perspective view showing an electronic apparatusaccording to another embodiment of the present invention, specifically,a desktop PC (Personal Computer).

The PC, denoted by reference numeral 50, includes a casing 63. The axialfan apparatus 10 (20) is arranged inside the casing 63. The axial fanapparatus 10 (20) is mounted to, for example, an opening portion (notshown) provided to a back surface 63 a of the casing 63. Alternatively,the axial fan apparatus 10 (20) is mounted to, for example, a heat sink57 connected to a CPU 55.

The electronic apparatus is not limited to a desktop PC as in the caseof the PC 50, but may be a server computer, a display apparatus, an AVdevice, a projector, a game device, a car navigation device, or otherelectronic products.

Embodiments of the present invention are not limited to the embodimentsas described above, but may be other various embodiments.

For example, in the axial fan apparatus 10, 20 according to theembodiments of the present invention, the slits 35 a are provided to thesubstantially entire circumference of the sidewall in thecircumferential direction. However, the plurality of slits 35 a may beprovided to a part of the sidewall corresponding to a predeterminedangle in the circumferential direction. Alternatively, two groups of theslits 35 a by the predetermined angle in the circumferential directionmay be 180°-symmetrically provided to the sidewall. Alternatively, threegroups of the slits 35 a by the predetermined angle in thecircumferential direction may be 120°-symmetrically provided to thesidewall. As described above, the slits 35 a can be provided in avarious manner.

It should be understood by those skilled in the art that variousmodifications, combinations, sub-combinations and alternations may occurdepending on design requirements and other factors insofar as they arewithin the scope of the appended claims or the equivalents thereof.

1. An axial fan apparatus, comprising; an axial-flow impeller capable ofrotating, that includes a plurality of blades inclined with respect to arotational axis direction; a drive unit that rotates the axial-flowimpeller; a housing mounted with the drive unit, the housing including(a) a sidewall provided around the axial-flow impeller, and (b) aplurality of slits that circulate gas in the sidewall and inclined withthe respect to the rotational axis direction in a direction opposed to adirection in which the plurality of blades incline, wherein, aninclination angle of the slits with respect to the rotational axisdirection is larger than 0° and smaller than 90°, and the sidewallincludes at least an annular inner circumferential surface.
 2. An axialfan apparatus, comprising: an axial-flow impeller capable of rotating toeffect a flow of gas to cool down one or more heat generators, theaxial-flow impeller including a plurality of blades inclined withrespect to a rotational axis direction; a drive unit that rotates theaxial-flow impeller; and a housing mounted with the drive unit, thehousing including an annular sidewall around the axial-flow impeller,the annular sidewall including a plurality of slits that enable thecirculation of the gas, the plurality of slits being adjacently spaced,defined entirely within the annular sidewall, and inclined with respectto the rotational axis direction in a direction opposed to a directionin which the plurality of blades incline, the axial-flow impeller andthe plurality of slits being configured to affect the flow of the gas tosuppress noise produced by the axial-flow impeller, a mount plateextends from a lower portion of the annular sidewall for mounting theaxial fan apparatus, wherein, an inclination angle of the slits withrespect to the rotational axis direction is larger than 0° and smallerthan 90°, and the sidewall includes at least an annular innercircumferential surface.